The present invention relates to an art of configuring the leads of a Lead Frame used in packaging integrated circuits, particularly for LOC (Lead on Chip) packages.
In conventional processes of packaging an IC (integrated circuit), a lead frame 1 as shown in FIG. 1 usually includes a plurality of leads separated into two groups respectively represented by reference numerals 11 and 12, the group represented by reference numeral 11 including a line of outward ends represented by reference numeral 13 and a line of inward ends represented by reference numeral 15, the group represented by reference numeral 12 including a line of outward ends represented by reference numeral 14 and a line of inward ends represented by reference numeral 16, the leads in the two groups stretching to the outside of the lead frame 1 in opposite directions. The two lines of inward ends 15 and 16, in order to match the size of an IC (under the lead frame 1, not shown in the figure), must be inside a quadrilateral region 17, and opposite to each other with a space 18 therebetween so that bonding wires 20 can be connected between bonding pad 100 of the IC and inward ends 15 or 16. As shown in FIG. 1, the two lines of inward ends 15 and 16 are inside a quadrilateral region 17 which is located in the central portion of lead frame 1, and are evenly dispersed between two parallel edges 171 and 173 of quadrilateral region 17 in two lines both perpendicular to the edges 171 and 173 while separated from each other by a distance 18. The distance 18 is to let bonding wire 20 pass therethrough so that the inward ends 15 and 16 can be connected to bonding pads 100 of an IC.
For more information about structures of a conventional lead frame used in Lead on Chip packages, reference to U.S. Pat. Nos. 5,545,920 and 5,872,398 shall be made.
To keep pace with the tendency of minimizing the size of an IC, the space available for accommodating leads 11 and 12 (also inward ends 15 an 16) in lead frame 1 is decreasing. For example, the pitch of bonding pads of an IC is reduced as a result of size reduction of the IC, and the pitch of leads as well as the gap 191 between adjacent inward ends of leads must be reduced accordingly, resulting in significant difficulty in packaging an IC subject to the tendency of minimizing the size of the IC, leading to higher failure rate and higher manufacturing cost. To respond to the tendency of minimizing the size of ICs (integrated circuits), the present invention provides schemes of changing the configuration of inward ends 15 and 16, so that the difficulty in the process of packaging ICs of smaller size arising from the requirement of smaller pitch of leads 11 or 12 (also smaller gap between adjacent inward ends 15 or 16) of a lead frame 1 can be avoided.
To keep pace with the tendency of increasing number of electrical connections with an IC, the space of a lead frame must be capable of accommodating more leads, resulting in significant difficulty in packaging an IC due to the inevitable reduction of inner lead pitch of a lead frame if size remains on the same scale, leading to higher failure rate and higher manufacturing cost. To respond to the tendency of requiring more electrical connections with an IC, the present invention provides schemes of changing the configuration of inward ends 15 and 16, so that the difficulty in the process of packaging an IC providing more electrical connections can be avoided.
An object of the present invention is to provide new configurations of a lead frame by which bigger inner lead pitches can be achieved without need of increasing the size of the lead frame, thereby the failure rate and manufacturing cost in the process of packaging ICs can be lowered, particularly the difficulty in packaging ICs of smaller size can be significantly eased.
Another object of the present invention is to immunize an IC packaging process against the difficulty resulting from smaller size of the lead frame or the IC to be packaged, or from larger number of leads/electrical connections of the lead frame or the IC to be packaged.
The present invention is characterized by arranging the inward ends of leads of a lead frame in unprecedented ways in order to realize bigger inner lead pitch (or bigger gap between adjacent inward ends) of a lead frame compared to a conventional one of equivalent size.
The word xe2x80x9cICxe2x80x9d in this disclosure means xe2x80x9cintegrated circuitxe2x80x9d, and the word xe2x80x9cICsxe2x80x9d means xe2x80x9cintegrated circuitsxe2x80x9d.
What is represented by the words xe2x80x9clead framexe2x80x9d in this disclosure is not limited to the popularly known lead frame. The lead frame in this disclosure represents any means capable of providing or supporting electrical conduction between at least an IC in a package and any device outside the package. A bonding surface of an IC in this disclosure means a surface from which the IC is electrically connected. For example, a bonding surface of an IC in the form of a chip is a surface having bonding pads thereon for electrical connection with the IC. What is represented by the word xe2x80x9cdispersexe2x80x9d in this disclosure includes the meaning of xe2x80x9cbe disposedxe2x80x9d.
A first aspect of the present invention may be represented by a lead frame for a process of packaging at least an IC, which comprises: a first group of leads; a second group of leads; and an IC corresponding region enclosed by a polygon (a quadrilateral corresponding to the pattern of an IC, or equivalent to the size or shape of a bonding surface of an IC, for example); wherein the lead includes at least an outward end and an inward end, the inward end being inside the IC corresponding region, the inward ends of the first group of leads facing and being spaced from the inward ends of the second group of leads; and wherein the first edge of the polygon is perpendicular to the second edge of the polygon, the third edge of the polygon parallels the first edge of the polygon, the inward ends disperse one by one between the first edge of the polygon and the third edge of the polygon (i.e., disperse one by one from the first edge of the polygon to the third edge of the polygon, or from the third edge of the polygon to the first edge of the polygon) in such a way that the further an arbitrary one of the inward ends is from the first edge of the polygon than another one of the inward ends, the nearer the arbitrary one of the inward ends is from the second edge of the polygon than the another one of the inward ends.
It can be seen the gap between any adjacent two of the inward ends of leads of either the first group or the second group in the lead frame according to the first aspect of the present invention can be significantly bigger than a corresponding gap (191 in FIG. 1) in a conventional lead frame of the same size scale, and the inner lead pitch of leads of either the first group or the second group according to the present invention can thus be significantly bigger. It is obvious the inner lead pitch of any two arbitrary leads of either the first group or the second group can be bigger than or at least equal to the gap between the inward ends of the two arbitrary leads.
If used in LOC packages, the inward ends of the first group of leads in the lead frame according to the first aspect of the present invention are spaced from those of the second group of leads by distances adequate for making electrical connection between the IC and the leads of the lead frame. For example, the bonding wires connecting the bonding pads of the IC and the leads of the lead frame must pass the space between the inward ends of the first group of leads and those of the second group of leads, therefore the distances between the inward ends of the first group of leads and those of the second group of leads are usually adequate for the bonding wires to be connected between the inward ends of the leads and the bonding pads of the IC. The distances between the inward ends of the first group of leads and those of the second group of leads may be uniform or vary with the locations of the inward ends, subject to the only condition that the space between the inward ends of the first group of leads and those of the second group of leads is adequate for electrically connecting therethrough the IC and the leads.
In the lead frame according to the first aspect of the present invention, the first group of leads may stretch to the outside of the lead frame in a first direction, and the second group of leads may stretch to the outside of the lead frame in a second direction different from or opposite to the first direction.
In the lead frame according to the first aspect of the present invention, the inward ends of the first group of leads may disperse along a first straight line, and the inward ends of the second group of leads may disperse along a second straight line either paralleling or not paralleling the first straight line. However, in the lead frame according to the first aspect of the present invention, the inward ends of the first group of leads do not necessarily disperse along a straight line, neither do the inward ends of the second group of leads necessarily disperse along a straight line.
In the lead frame according to the first aspect of the present invention, the IC corresponding region may be a plane matching the pattern of the IC or a bonding surface of the IC.
A second aspect of the present invention may be represented by a lead frame for a process of packaging at least an IC, which comprises: a first group of leads; a second group of leads; and an IC corresponding region (a 3-dimensional space) enclosed by a hexahedron which, for example, has a bottom surface corresponding to a bonding surface of an IC, and is rather small in height; wherein the lead includes at least an outward end and an inward end, the inward ends being inside the IC corresponding region, the inward ends of the first group of leads facing and being spaced from the inward ends of the second group of leads; and wherein the first surface of the hexahedron is perpendicular to the second surface of the hexahedron, the third surface of the hexahedron parallels the first surface of the hexahedron, the inward ends disperse one by one between the first surface and the third surface (i.e., disperse one by one from the first edge of the polygon to the third edge of the polygon, or from the third edge of the polygon to the first edge of the polygon) in such a way that the further an arbitrary one of the inward ends is from the first surface of the hexahedron than another one of the inward ends, the nearer the arbitrary one of the inward ends is from the second surface of the hexahedron than the another one of the inward ends.
It can be seen the gap between any adjacent two of the inward ends of leads of either the first group or the second group in the lead frame according to the second aspect of the present invention can be significantly bigger than a corresponding gap (191 in FIG. 1) in a conventional lead frame of the same size scale, and the inner lead pitch of leads of either group according to the present invention can thus be significantly bigger. Again it is obvious the inner lead pitch of any two arbitrary leads of either group can be bigger than or at least equal to the gap between the inward ends of the two arbitrary leads.
If used in LOC packages, the inward ends of the first group of leads in the lead frame according to the second aspect of the present invention, similar to those in the lead frame according to the first aspect of the present invention, are spaced from the inward ends of the second group of leads by distances adequate for making electrical connection between the IC and the leads of the lead frame. For example, the bonding wires between the bonding pads of the IC and the leads of the lead frame must pass the space between the inward ends of the first group of leads and those of the second group of leads, therefore the distances between the inward ends of the first group of leads and those of the second group of leads are usually adequate for the bonding wires to be connected between the inward ends and of leads and the bonding pads of the IC. The distances between the inward ends of the first group of leads and those of the second group of leads, similar to those according to the first aspect of the present invention, may be uniform or vary with the locations of the inward ends, subject to the only condition that the space (not limited to two dimensions here) between the inward ends of the first group of leads and those of the second group of leads is adequate for electrically connecting therethrough the IC and the leads.
In the lead frame according to the second aspect of the present invention, the first group of leads may stretch to the outside of the lead frame in a first direction, and the second group of leads may stretch to the outside of the lead frame in a second direction different from or opposite to the first direction.
In the lead frame according to the second aspect of the present invention, the inward ends of the first group of leads may disperse along a first plane, and the inward ends of the second group of leads may disperse along a second plane either paralleling or not paralleling the first plane. However, in the lead frame according to the second aspect of the present invention, the inward ends of the first group of leads do not necessarily disperse along a plane, neither do the inward ends of the second group of leads necessarily disperse along a plane.
In the lead frame according to the second aspect of the present invention, any surface of the IC corresponding region may be a plane. For example, the first, the second, and the third surfaces as well as and the aforementioned xe2x80x9cbottom surfacexe2x80x9d of the IC corresponding region are planes, wherein the aforementioned xe2x80x9cbottom surfacexe2x80x9d may be perpendicular to the second surface and be a plane facing a bonding surface of an IC, with its size or pattern or shape equivalent to the bonding surface of an IC. The aforementioned xe2x80x9cbottom surfacexe2x80x9d may even be the bonding surface of an IC.
A third aspect of the present invention may be represented by a lead frame for a process of packaging at least an IC, which comprises: a plurality of leads each including at least an outward end and an inward end; and an IC corresponding region (a region enclosed by a polygon such as a quadrilateral corresponding to the pattern of an IC, or equivalent to the size or shape of a bonding surface of an IC, for example); wherein the inward ends are inside the IC corresponding region, the first edge of the polygon is perpendicular to the second edge of the polygon, the third edge of the polygon parallels the first edge of the polygon, and the inward ends disperse one by one between the first edge and the third edge (i.e., disperse one by one from the first edge of the polygon to the third edge of the polygon, or from the third edge of the polygon to the first edge of the polygon) in such a way that the further an arbitrary one of the inward ends is from the first edge of the polygon than another one of the inward ends, the nearer the arbitrary one of the inward ends is from the second edge of the polygon than the another one of the inward ends.
According to the third aspect of the present invention, the difficulty to provide a lead frame with all leads thereof stretch in the same direction to the outside of the lead frame can be significantly eased. This is because the gap between any two adjacent inward ends of the leads according to the present invention can be significantly augmented under the condition the size of the lead frame and the number of leads of the lead frame remain the same. The inner lead pitch, as a result, can be significantly augmented for a lead frame with the same size and the same number of leads. All of the leads of the lead frame according to the third aspect of the present invention may stretch to the outside of the lead frame in the same direction without suffering the difficulty of dealing with smaller inner lead pitch, and without need of bigger size of lead frame. All of the leads of the lead frame according to the third aspect of the present invention may stretch to the outside of the lead frame in a direction perpendicular to the second edge of the polygon, for example.
It must be noted the IC corresponding region according to the third aspect of the present invention is not limited to a 2-dimensional space, and can be a 3-dimensional space enclosed by a hexahedron such as the one defined in the second aspect of the present invention, i.e., the inward ends of leads of the lead frame do not necessarily disperse along a line, nor do they necessarily disperse along a plane. Actually the lead frame according to the second aspect of the present invention may include one instead of two groups of leads, all the leads stretching to the outside of the leads frame in the same direction, the inward ends of the leads being configured in the same way as the third aspect of the present invention.
A fourth aspect of the present invention may be represented by a lead frame for a process of packaging at least an IC, which comprises: a plurality of leads each including at least an outward end and an inward end; and an IC corresponding region enclosed by a polygon (a quadrilateral, for example) including a first edge, a second edge, a third edge, and a fourth edge, the first edge paralleling the third edge, the second edge paralleling the fourth edge, the first edge and the second edge constituting an obtuse angle (an angle smaller than 180xc2x0 while larger than 90xc2x0); wherein the leads are separated into two groups respectively having the inward ends thereof dispersing along the second edge and the fourth edge.
As can be understood from the first aspect of the present invention, the gap between any adjacent two inward ends of leads of each of the two groups in the lead frame according to the fourth aspect of the present invention can be significantly bigger than a corresponding gap (191 in FIG. 1) in a conventional lead frame of the same size scale, and the inner lead pitch of leads of each group according to the present invention can thus be significantly bigger.
Obviously the two groups of leads in the lead frame according to the fourth aspect of the present invention may respectively stretch to the outside of the lead frame in different or opposite directions.